1. Field of the Invention
The invention relates to a medium conveying apparatus, a medium feed control method, and an image forming apparatus using the control method and, more particularly, to a control method of preventing an overlap-feed of recording media and an image forming apparatus using the control method.
2. Related Background Art
In recent years, various image forming apparatuses have been developed and there are many kinds of recording media which are used in the image forming apparatuses. Therefore, development of a technique of a sheet feeding mechanism for feeding the optimum recording medium is also a significant subject (for example, refer to JP-A-2002-46882). Particularly, in an image forming apparatus for forming a full-color image, since image quality is improved if the image is recorded onto thick paper, it is demanded to accurately convey the recording media of various thicknesses. According to the related art, a medium thickness sensor for detecting the thickness of recording medium is arranged on a conveying path and, if the thickness detected by the medium thickness sensor exceeds a predetermined thickness, it is determined that an overlap-feed has occurred, so that the conveyance of the recording media is stopped. Further, the recording media whose conveyance has been stopped are temporarily returned into a paper feeding apparatus and supplied to the conveying path again. However, even if they were temporarily returned into the paper feeding apparatus and supplied to the conveying path again, it is often repetitively determined that the overlap-feed has occurred. In such a case, the recovery operation is repeated many times and the conveyance of the recording media is stopped (a jam error is displayed) eventually.
It is, therefore, a problem to be solved that in the conventional medium conveying apparatus, if the thickness detected by the medium thickness sensor exceeds the predetermined thickness, it is determined that the overlap-feed has occurred, so that the recording media are temporarily returned into the paper feeding apparatus and supplied to the conveying path again, and in such a case, the recovery operation is often repeated many times and the conveyance of the recording media is stopped (a jam error is displayed) eventually.